[Fire TV Android Development] rbox:
Here are prerooted stock images for use with my recovery. Note that these contain addon.d support, so any 3rd party things you install to /system need an addon.d script to be retained between flashes.

Managing Stock Recovery

Starting with 5.0.5_r3, stock recovery gets disabled. This means you cannot reboot in to stock recovery manually or automatically because of a system update. This will make it safer for people who forget to disable updates. You should still disable updates though. If for whatever reason, you want to reenable it, or verify it is disabled, you can use the manage_recovery program. Under normal circumstances, you should never need to use manage_recovery.

Connect to adb and start a shell

Switch to root with su

Run manage_recovery (if you do not run su first, it will seem to run, but won't actually be able to do anything)

manage_recovery

There are 3 different scenarios that manage_recovery will detect and prompt for.

The first is when stock recovery is disabled, it will look like this:

Checking current stock recovery status... NOT STOCK
Checking for reason... DISABLED
Stock recovery is currently disabled,
Would you like to enable it?
Type 'yes' to enable it, anything else to quit.

The second is when a stock recovery is flashed that does not match the current system version:

Checking current stock recovery status... NOT STOCK
Checking for reason... WRONG VERSION
Would you like to disable stock recovery?
Type 'yes' to disable it, anything else to quit.

And finally, the third is when stock recovery is enabled and the correct version:

Checking current stock recovery status... STOCK
Would you like to disable stock recovery?
Type 'yes' to disable it, anything else to quit.

After changing the recovery status, you can run the program again to verify it changed.

WARNING: DO NOT FLASH 5.0.5.1 OR EARLIER IF YOU STARTED WITH VERSION 5.2.1.0 OR LATER

NOTE: If you were at 5.2.6.6 or below, you MUST flash 5.2.6.7 before going to 5.2.6.8 or later.

Changelog and Downloads:

December 26, 2020 - 5.2.7.6_r1 (md5sum: 01178aecf55cd895cbfdeb64d5a19e62)

July 4, 2020 - 5.2.7.3_r1 (md5sum: 875436574974c3603aef179b898a4c60)

December 7, 2019 - 5.2.7.2_r1 (md5sum: b91c6b596ef5daae085ddf08c1c504e5)

September 21, 2019 - 5.2.7.1_r1 (md5sum: 0d72e930cee2652d324d2fceebdd4202)

June 29, 2019 - 5.2.7.0_r1 (md5sum: 1e402185cefb91276d811f1321494863)

March 30, 2019 - 5.2.6.9_r1 (md5sum: a3e23a7f337346a4638f8c8895632046)

February 10, 2019 - 5.2.6.8_r1 (md5sum: bd0daa677635e04e368d1b2b235e03e9)

December 2, 2018 - 5.2.6.7_r2 (md5sum: b50a1fddb3e01c18c353195c9f7f50cd)

This ROM contains updated DRM firmware.

November 27, 2018 - 5.2.6.7_r1 (md5sum: b0ee16b57b37a934778ca1436f29916a)

This ROM contains updated DRM firmware.

September 28, 2018 - 5.2.6.6_r1 (md5sum: 37ce0c6dda850fa2d462835496b68576)

June 24, 2018 - 5.2.6.3_r1 (md5sum: 08982269022c01c9a1eac8ff94adf637)

January 28, 2018 - 5.2.6.2_r1 (md5sum: 0967de2a707f173ca8715356a20ea88e)

October 8, 2017 - 5.2.6.0_r1 (md5sum: 84eedbb2e9fd4b57679747ecb8fae797)

July 27, 2017 - 5.2.4.2_r2 (md5sum: a96e73478cdbe8659f6758a5d27b4738)

This includes updated firmware to fix Hulu and HBO.

July 3, 2017 - 5.2.4.2_r1 (md5sum: 0719fde0db90702c2407461003217977)

May 1, 2017 - 5.2.4.1_r1 (md5sum: 64915fceb4e7d1c0de9d1ef625db48e7)

December 10, 2016 - 5.2.4.0_r1 (md5sum: 77af47d3c43fe79e82740d0cc0c4bce5)

September 10, 2016 - 5.2.1.1_r1 (md5sum: fd7c06bce26d4aa611eef402ef156322)

July 4, 2016 - 5.2.1.0_r2 (md5sum: a69981f6d4dce77cf1f9907f8a39b391)

This is the same as the previous 5.2.1.0, just with the updated version that Amazon released.

June 1, 2016 - 5.2.1.0_r1 (md5sum: 81693eae0ce3b497cf425691bc4ad041)

This includes 2ndinit version dee776 and TWRP version 3.0.0-5.

April 8, 2016 - 5.0.5.1_r1 (md5sum: c6d8a11b7ca7a0b45a38af4f9f70cf2d)

The updated TWRP in this version should disable auto flashing amazon updates.

This includes 2ndinit version dee776 and TWRP version 3.0.0-5.

February 14, 2016 - 5.0.5_r4 (md5sum: 9145c8f6d52fda2c3cfdd1d091bcb331)

The updated TWRP in this version should fix the issues certain keyboards were having.

This includes 2ndinit version dee776 and TWRP version 3.0.0-4.

February 13, 2016 - 5.0.5_r3(md5sum: 92d08a12d240cf9bf6d25005a65bd82d)

Starting with this update, stock recovery will be disabled to prevent stock updates from being flashed. Please refer to the instructions above for managing stock recovery.

This includes 2ndinit version dee776 and TWRP version 3.0.0-3. Because this comes with a newer 2ndinit version, do not flash an older recovery package. Doing so will disable su.

February 12, 2016 - 5.0.5_r2

OTA updates are permanently disabled, otherwise the same as r1.

[*]

This breaks booting with a factory reset.

February 12, 2016 - 5.0.5_r1(md5sum: 211a15f949e317b02c637b2927a7c8ba)

This includes 2ndinit version 743aa4 and TWRP version 3.0.0-3.

February 8, 2016 - 5.0.4_r2(md5sum: ebcecf89e9b81c02f22ed2706fe5f796)

This comes with TWRP 3.0.0-2

This comes with the same 2ndinit version

February 6, 2016 - 5.0.4_r1(md5sum: 87ce4f7802d21bd1f14c45d473783713)

This comes with 2ndinit version fe3362 and recovery version 3.0.0-1

February 6, 2016 - 5.0.3.1_r1(md5sum: e38d66dce235c9c0122dfbde2db5a6b6)

This comes with 2ndinit version fe3362 and recovery version 3.0.0-1